You brute! Thus began a letter written to Sir Arthur Conan Doyle protesting at the death of Sherlock Holmes in The Final Problem.

The Strand Magazine subsequently lost 20,000 subscribers and Doyle gained a whole postbag of hatemail. With fans like these, eh? Of course, Holmes was back within a decade and he has never left us since.

Guinness World Records lists Holmes as the most portrayed literary human character on screen (Dracula is first but undead) – and then you have the stage adaptations, the radio plays, the computer games, the comic books.From four novels and 56 short stories, one writer created an entire cultural universe.

As the author of two Holmes novels – The House of Silk and Moriarty – Anthony Horowitz is the perfect guide to the world of Conan Doyle.

And remember: when you have eliminated the impossible, what remains, however improbable, must be the truth…

Why should you read Sherlock Holmes? 

First of all, this is where all modern detective fiction begins. The birth of the modern detective story is with Sherlock Holmes.

The stories are, like the Bond novels, waiting to be discovered: the quality of the writing, the joy of the world, the uniqueness of what has been created. They may surprise you because there are very few murders in Sherlock, the stories are much more peculiar than that.

Doyle is an extraordinarily clever writer. He's a sort of gothic romanticist. His descriptions of London, the atmosphere of the world, the sense of the streets, the fog, all that stuff. It's very, very elevated. And it's not what you think of when you watch Robert Downey Jr or even Benedict Cumberbatch, so they will delight you. They will just delight you and they will surprise you.

To get the obvious stuff out of the way: the literary Sherlock doesn’t wear a deerstalker and never says, “Elementary, my dear Watson…” 

That is absolutely correct. There are these little mistakes that have been made. Some creep into the canon. 

He does, however, take cocaine...

Not very often. The Sign of Four begins with Watson concerned about Holmes's cocaine use. He does keep cocaine in a Turkish slipper on the mantelpiece. He takes cocaine when he's bored. 

After the Reichenbach Fall, people were actually wearing black in the street, they were so upset about Sherlock's death

Obviously today Sherlock Holmes is a global brand – but his popularity in Victorian England was almost impossible to comprehend... 

People wore black when he died. After the Reichenbach Fall, people were actually wearing black in the street, they were so upset about his death. Yes, he was an absolutely huge phenomenon, the Harry Potter of this time, I suppose. And made Doyle very wealthy. 

What has always fascinated me is Doyle's misgivings about the character, the fact that he thought Holmes beneath him, hated him, wanted to get rid of him, and that it always makes me smile. Doyle thought that sort of murder mystery, detective fiction, whatever you want to call it, was beneath him. That it was somehow too trite. 

He wanted people to read his Gothic, his historical romances. So books like the White Company and Micah Clarke, which have now more or less been completely forgotten, are the books that he staked his reputation on. He killed Holmes off very happily in The Final Problem and only brought him back for financial reasons. 

Holmes tends to be portrayed as an emotionally stunted sociopath – yet the literary Sherlock is a relatively warm, empathetic man comfortable in his own skin…

I'm not sure that's entirely true. If you look at what Watson writes about Holmes, particularly in the earlier books such as A Study in Scarlet, he is actually quite an irritating human being. Cold, aloof, the flat's untidy.

There are a couple of occasions only where he worries about Watson. Watson is hurt in one of the stories and Holmes rushes over and is quite emotional for a brief moment. But by and large, he is quite a difficult character.

The genius of the books is that if you or I met Holmes I don't think we'd like him, but we only meet him through Watson, who absolutely adores him; who is aware of his failings as a human being but is also in admiration of his detective abilities and his talents and his intellect. And it is Watson's voice and Watson's friendship that makes the books palatable. 

Sherlock Holmes and Dr Watson

Hound of the Baskervilles aside, the short stories tend to be more celebrated than the novels – and none of the four novels are particularly long. Is there something about Holmes that makes him a natural for short stories?

Yes, I found when I wrote The House of Silk one of the biggest problems I had was expanding the world of Holmes to 90,000 words. A modern novel is 90,000 words; the longest Holmes story is about 44,000 words. These are not classic murder mystery stories with lots of suspects. They're much more peculiar than that. 

What you normally get is a situation, which is very difficult to explain, which over the course of about 15 or 20 pages, Holmes explains. The stories are all about incidents. The novellas go a bit bigger, but even they tend to be quite small.

The scope might be big: the characters might have come to England from America, where they've been involved with Mormons and where there is some kind of conspiracy to kill them. But the killing is quite a small incident. So that's why they are better suited to short stories. 

If you go for the greatest of the short stories, a man trying to kill somebody with a snake or somebody being fooled into believing their red hair is somehow significant: these are big ideas, but they don't have very far to travel. 

These are little ideas, but they're great ideas. The six busts of Napoleon, the blue carbuncle in the Christmas pudding. Incidents. They're all incidents.

And because they're so rarified, the names of the characters, the types of characters, the world in which they inhabit is so peculiar and gothic, I think less is more. If you expanded it too much, you'd end up wallowing in it. 

More than any fictional character, Holmes has blurred into history: he’s as much a part of his era as Queen Victoria or Jack the Ripper. Why would you say that is?

Holmes has an interesting relationship with history. We look on late Victorian England now through the prism that Conan Doyle created. That's one of his greatest talents as a writer. This Gothic romance, his ability to conjure up a world. 

I can only think of one author where you can say just five words and immediately wallow in the world they've created. So I say to you: fog, gas lamp, growler, Stradivarius and you are there immediately. It's all around you, you feel it and you know it and you inhabit it and you sort of love it. 

Being British, it's in our bloodstream. We can't get away from it now. And that was Doyle’s genius as a writer, even more than the plots themselves. 

Sir Arthur Conan Doyle

And when you’ve written as Doyle, do you engage entirely with his world, or attempt to inject some modern sensibilities? And how do you capture the voice of Victorian England from the 21st century?  

I'm not interested in doing anything other than living inside his world. I do exactly what Doyle did. I read the books. I try to understand what he wanted to achieve, how he achieved it. And although again, I'm not as good a writer as Doyle, I do everything in my power to write like him. So I obey all his rules. 

It helps that throughout my life I read 19th century literature: all my favourite authors are 19th century authors: Dickens to Gissing to Orwell, trending into the 20th century but then Doyle himself is an early 20th century writer too. But I feel that I've lived part of my life in the 19th century and therefore I don't find it difficult to assume the language and the sensibility at the time. 

Then I use a lot of research. There are some wonderful websites: Victorian London is a fantastic website of details about almost anything you want to know about Victorian London – from what people smoked, what they wore, what they ate, how often they had sex. It's all there. 

The classic Holmes scene involves Holmes making incisive observations based on a stranger’s appearance. How do you create those scenes – ensuring the deductions are brilliant yet believable? 

It's quite interesting to look at how Doyle does it, because actually the amount of clues you can have are quite limited. I can't remember how many short stories Holmes construes something from the mud on somebody's foot. 

So it might be on the right hand side of the foot, not the left hand side of the foot. It might be a certain type of mud or it might have dried when it's actually still raining. But the amount of clues – the stain on the cuff or the tie, the type of clothing, etc – are few and far between. 

Moriarty is one of the central characters to the Holmes mythos: yet the Professor only appears in a single story. Why did he have such an impact? 

Moriarty is a creation of great genius. The reason why he is so profoundly successful and powerful is, first of all, his name. Doyle was brilliant at naming characters. And Moriarty is just the greatest name for a villain, obviously with a morgue in there and mortality and such, but not quite. Funnily enough, it's the name of a boy who was at school with Doyle. That's where he took the name from. But it's a brilliant choice. 

So little is known about him – he appears in one story and is mentioned in two more – but it's enough. Holmes has such great respect for him: there's all that stuff in The Final Problem where he bigs him up and gives this background to him. It's funny that he's managed to get through quite a lot of stories barely mentioning him, but suddenly every crime in London seems to be coming home to this one character. It's just a fantastic creation. 

If we knew more about him, how he operated, what he did for a living before he became a criminal, he might be less powerful. 

My favourite fan theory is that Moriarty didn’t exist. He was dreamt up by Holmes in a cocaine-addiction mania, desperate to find a worthy rival…  

There have been various versions of that. In The Seven Percent Solution, which is a really very, very good Holmes continuation, Moriarty turns out to be the teacher at his school whom he has exercised and turned into his nemesis. He doesn't really exist, and he's a perfectly blameless character. 

I loved writing my book, Moriarity, because there is so little known. It was a joy to be able to invent my own world. With The House of Silk, I felt I had done the best work I could do and there was nothing left to do. I'd done all the tricks, I'd done "Elementary, my dear Watson", I'd done all the Holmes scenes you expect. And I thought, well, I can't do a second Holmes now because I've got nowhere left to go. So let's go to the other side of the coin to do Moriarty. 

The thought that entered my head was this: Moriarty is the most evil person in the world. Is it possible to write a book that is as evil as him? So that was the plan. I'll write an evil book. And that's what I did. 

The Death of Sherlock Holmes by Sidney Paget

The Holmes books are notorious for their small inconsistencies – why is Watson called John, but sometimes James by his wife?  Why are both Professor Moriarty and his brother called James? How far, if at all, do you try to unravel these Conan Doyle lapses?

Well, the whole of Moriarty is based on the impossibility of Holmes's survival. Doyle kills Holmes in The Final Problem and then brings him back in The Empty House. but if you look at the explanation of what happened at the Reichenbach Falls, none of it makes any sense. It's all completely nonsensical. Therefore the joy of writing Moriarty was to pull that to pieces and say it's nonsense. And then I went to work out what really happened. 

Doyle, who is a great writer and a much better writer than me, made loads of mistakes. I mean, The Speckled Band has got wonderful mistakes in it. For example, snakes can't climb ropes. They're also deaf. So they can't hear a musical chord. 

There's another lovely little mistake in The Adventure of the Priory School: Holmes follows a bicycle track. And of course, it's actually impossible to follow a bicycle track because you don't know which way it's going. 

In one book, Watson has been shot in the shoulder in the Afghan war, in another book the wound is in his leg. And I often joke that he must be kneeling in an uncomfortable position and the bullet went through his shoulder into his leg. And that's how he's got the two wounds. But it's actually a mistake and I like it. It's great that Doyle's greatness is not damaged by his occasional transgressions. 

Which stories would you recommend a first-time reader picking up? 

Wow, that's a tricky one. I guess you have to go for A Scandal in Bohemia because it's such a classic story. I've always loved The Dying Detective, it's one of my favourite stories. Charles Augustus Milverton, wonderful, wonderful character and therefore one of my favourite stories. And I suppose The Speckled Band because it's so gothic and so classic. 

Which is the most ingenious plot in Sherlock Holmes?

I would go for The Norwood Builder. It's a really good plot with a really good twist. 

Favourite Holmes quip? 

I think it would be when you have eliminated the impossible, whatever remains, however improbable, must be the truth.” [From The Sign of Four.]

Best one-off character in the canon? 

Charles Augustus Milverton. 

Best overall story? 

The Red Headed League. 

With a Mind to Kill, the third James Bond novel by Anthony Horowitz, will be published on 26 May.